I see that this topic has been addressed previously, but not very recently, so maybe there's a new solution by now. My 2002 P5, 189K miles, shows P0421 code indicating a poorly performing pre-cat. I tried CataClean and the isolating the rear 02 sensor, both of which did nothing to improve things (and now I'm out an 02 sensor!).
Is it worth buying new, CA-compliant cat at this point? The dealer wants $1200 (likely more than the car is worth) and an independent shop wants $800 to replace it, although they will install one bought elsewhere for $75. And what happens if the cat is replaced and the code still appears?
Please forgive what must seem like 'duh' questions, but I'm new here and don't really know the protocol.
Thanks!
Is it worth buying new, CA-compliant cat at this point? The dealer wants $1200 (likely more than the car is worth) and an independent shop wants $800 to replace it, although they will install one bought elsewhere for $75. And what happens if the cat is replaced and the code still appears?
Please forgive what must seem like 'duh' questions, but I'm new here and don't really know the protocol.
Thanks!